This paper describes innovative technology for the rapid and accurate measurement of degassed acid conductivity (DAC) which is the culmination of 21 years of scientific research into the measurement of dissolved carbon dioxide and its removal from the sample to speed up the return to service of the turbine after an outage.

During the 1980s, a utility was concerned about the lack of boiler corrosion protection during idle periods when cycling for economic reasons. This led to a search for better ways to protect the boiler waterside and still meet the needs of the load dispatch control center. With system load requirements dictating short periods of shutdown for some units, a challenging dilemma for the boiler water chemistry program developed due to the reluctance on the part of those involved with operations to call the economic shutdowns "storage outages." The duration of the economic shutdowns often varied between overnight to 40 days and seasonally could be as long as 6 months. Wet storage treatment was not considered until the boiler had been off-line for seven days. The declining pressure method of storage utilizes the residual boiler temperature and pressure of ~1.38 MPa (~200 psi) to thermally mix a low level storage dosage that is injected with the existing boiler water chemical feed system. The effectiveness of the boiler storage program has been evaluated over the past 20 years when determining the need to chemically clean the boiler. One of the tools investigated was the use of the ultrasonic technique to measure the waterwall oxide thickness in high heat areas. Confirmation by tube specimen deposit analyses yielded mixed results although the ultrasonic testing did prove to be helpful in selecting the tube with the highest potential for the most deposition. A recent study found that the Kyushu ultrasonic testing method could provide accurate oxide thickness measurements of tube oxides.

Ontario Power Generation (OPG; formerly Ontario Hydro) is a provincially owned Canadian utility that has provided better than 80 % of the province's electricity for the past 100 years. OPG's current mix of assets includes several peaking fossil fuel plants (primarily coal-fired drum units). This paper reviews the current practices for short- and medium-term lay-up of these peaking units. It includes the key return to service parameters and practices used at OPG, and reviews the relative performance of the units following these practices. The paper focuses on the water chemistry aspects of the lay-up and return to service, in particular on chemical parameter monitoring and chemical dosing practices in addition to the use of chemical control equipment such as condensate polishers. The paper focuses on two-shifting, weekend outage turnarounds and planned maintenance outage turnarounds, but it also covers indefinite length non-maintenance outages which can last up to several months.

A reduction in the dissolved oxygen concentration level of the primary heat transport (PHT) system was observed after a changeover from helium to nitrogen in the cover gas of the D2O storage tanks of PHT systems of Indian pressurized heavy water nuclear reactors (PHWRs). Radiolysis of the dissolved nitrogen to form atomic nitrogen and its reaction with water and OH radicals leads to the formation of NO and NH3, which results in scavenging of the dissolved oxygen. However, the concentration of corrosive nitrate formed in this process needs to be minimized. Enhancing the coolant purification flow for the removal of nitrate imposes a heat loss penalty, resulting in a reduction in power generation. On the other hand, hydrogen injection to the system, which suppresses the concentration of corrosive nitrate species, seems advantageous. Thus, a combination of nitrogen as a cover gas in the PHT heavy water storage tank with continued hydrogen injection is recommended to suppress the corrosive effects due to dissolved oxygen and nitrate while retaining the benefits due to the substitution of helium with nitrogen.

Oxides and deposits on the internal surfaces of boiler tubes reduce heat transfer and increase corrosion in waterwall tubes and creep in superheater tubes. To improve the heat transfer, boiler efficiency and availability, chemical cleaning of boilers is regularly carried out by interconnecting the waterwall and economizer tubes in circuit. We have carried out the chemical cleaning of more than 15 boilers of the National Thermal Power Corporation and other utilities in India. The chemical cleaning was carried out mainly by hydrochloric acid along with other chemicals. Single stage, double stage or multi stage chemical cleaning was carried out depending upon the quantity, type and quality of internal deposit in water wall tubes. Recently, two old boilers (100 MW and 200 MW) were cleaned by two-stage and multistage cleaning in one of the stations of the National Thermal Power Corporation. Improvement in the unit heat rate ranging from 135–220 kcal · kW^–1 · h^–1 was observed after the overhaul and chemical cleaning of the boilers, and the boiler efficiency was increased in the range of 1.3–2.3 %. This paper discusses the reasons for the increase in internal deposits in boiler tubes, sampling and internal deposit quantity measurement, criteria for post-operational chemical cleaning, solvent selection, and efficiency measurement and its advantages.

Newly constructed thermal power plants have typically been subjected to chemical cleaning before the start of operations in order to remove oily substances and metal oxidation scale which may have accumulated during the manufacturing process. In this paper steps taken to save time and costs in regard to this phase of commissioning by Mitsubishi Heavy Industries, Ltd. are presented. These include quality control improvements during construction/manufacturing and the proprietary "Single Stage Chemical Cleaning Method". The results of investigations are discussed which show these developments to be very successful in the simplification of chemical cleaning steps during plant construction. In some cases chemical cleaning is no longer considered necessary at all.